Cave pollen taphonomy in Kurdish Iraq

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Abstract

This thesis aims to understand the mechanisms involved in pollen transport and deposition in cave environments and the influence of different factors on the composition of the pollen assemblage, with special reference to the problem of the Neanderthal ‘Flower burial’ at Shanidar Cave, Kurdish Iraq. Limited systematic taphonomic work has been done in cave environments, with most of the studies on an ad hoc basis. However, the number of interconnected factors acting on pollen transport, deposition and accumulation in this kind of environments implies that models used for open-air sites are inadequate and demonstrates the need for further taphonomic studies. Surface samples from six caves located in the Zagros Mountains of Kurdish Iraq were collected along front-back transects and outside for comparison in order to evaluate the distribution of anemophilous and entomophilous taxa in relation to the sample location. Additional surface samples were collected from Shanidar Cave along a side to side and perimeter transects to better evaluate the pollen distribution. Water, airfall and animal dung samples were also collected to investigate the influence of those factors in pollen transport. Finally, stratigraphic samples collected during the excavation at the site were analysed for pollen and for particle size distribution. Results show that simple sac-like caves with little or no influence of factors such as water, humans and animals are characterised by broadly predictable patterns of pollen distribution with a positive correlation between anemophilous pollen and vicinity to the cave entrance and entomophilous pollen and distance from the cave entrance. Caves with active biotic vectors and/or more complex geomorphology show instead more irregular patterns. Cave SLS203 presents an inverse anemophilous/entomophilous distribution that is likely to be related to its geomorphological complexity (a second entrance at the back of the cave influencing the air circulation) and to the presence of animals. Shanidar Cave presents a very irregular distribution which is likely to reflect a combination of factors such as the mixing of surface sediments caused by the tourists visiting the site, the pollen transported by animals and that moved by the wind. Other factors, such as water input and cave entrance flora, seem not to play an important role in ii Kurdish Iraq, while they appear to strongly influence pollen distribution in caves elsewhere (e.g. Coles, 1988; Simpson, 2006). The stratigraphic samples were sterile or contained few pollen grains, probably because the aeolian nature of the sediments, deposited during stadials, with low pollen deposition and high sediment influx. Finally, clumps of pollen of both anemophilous and entomophilous taxa have been found for different taxa in all the caves. Leroi-Gourhan (1975) had suggested that similar clumps found in the vicinity of Shanidar IV remains were evidence for burial with flowers but their presence on the surface demonstrates that they can occur naturally and that other explanations should be considered. Moreover, the high amount of Lactuceae and the presence of older pollen grains in her samples suggest a strong taphonomic imprint not necessarily resulting from anthropogenic activity.